Biocidal bicyclic polyoxymethyleneoxazolidines

ABSTRACT

Biocidal compositions useful in controlling the growth of bacteria and fungi in aqueous surface coatings are aqueous solutions that contain from 20 percent to 80 percent by weight of a bicyclic polyoxymethyleneoxazolidine having the structural formula ##EQU1## wherein each R represents hydrogen, alkyl of 1 to 6 carbon atoms, phenyl, halophenyl, or --(CH 2  O) m  CH 2  OH; m represents a number in the range of 0 to 2; and n represents a number in the range of 1 to 4.

This is a division of our copending application Ser. No. 447,797, which was filed on Mar. 4, 1974 and which is now U.S. Pat. No. 3,890,264.

This invention relates to a certain bicyclic polyoxymethyleneoxazolidines. It further relates to biocidal compositions that are aqueous solutions which contain from 20 to 80 percent by weight of these bicyclic polyoxymethyleneoxazolidines and which are useful in controlling the growth of bacteria and fungi in aqueous surface-coating compositions.

It is well known in the art that paints and varnishes often have inadequate resistance to the action of microorganisms. Some of these coating compositions, sucn as enamels and house paints, contain as their resinous binders drying oils, oleoresinous varnishes, or alkyd resins, which are subject to attack by fungi and bacteria. Others, for example, aqueous dispersions of water-insoluble synthetic linear polymers, generally contain as plasticizers and thickeners materials that have their origin in animal or vegetable sources and that render the compositions susceptible to mildew. The resulting deterioration of the surface-coating compositions seriously hinders their full scale utilization, particularly in those areas and in those applications that are conducive to such attack.

Various biocidal materials have been suggested for use in surface-coating compositions, but none has proven entirely satisfactory in this application. Some do not provide the required prolonged protection against attack by microorganisms, while others undergo sulfide staining and still others hydrolyze in alkaline aqueous paint systems or separate from the applied coating by migration, volatilization, or leaching after the coating has been spread in a thin layer over the surface to be protected. Some biocidal materials cause the coating compositions to gel or impart color or odor to them.

This invention relates to biocides that are of particular value in surface-coating compositions. These biocides, which are stable in aqueous solutions, which are thoroughly compatible with the resinous binders that commonly are used in surface-coating compositions, and which are resistant to sulfide staining, provide excellent and prolonged resistance to deterioration resulting from attack by bacteria, fungi, and other microorganisms without adversely affecting the color, pH, viscosity, and other physical properties of the surface-coating compositions.

The biocidal compounds of this invention have the structural formula ##EQU2## wherein each R represents hydrogen, alkyl of 1 to 6 carbon atoms, phenyl, halophenyl, or --(CH₂ O)_(m) CH₂ OH; m represents a number in the range of 0 to 2; and n! represents a number in the range of 1 to 4.

Illustrative of these polyoxymethyleneoxazolidines are the following: 5-[hydroxymethyl-di(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 5-[hydroxymethyl-tri(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 2-phenyl-5-[hydroxymethyl-tetra(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 2,8-bis(α-chloroethyl)-5-[hydroxymethyl-penta(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 2,8-bis(p-chlorophenyl)-5-[hydroxymethyl-tri(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 2-hydroxymethyl-5-[hydroxymethyl-tetra(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, 2,8-bis(2-ethylbutyl)-5-[hydroxymethyl-tri(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, and 2,8-bis(hydroxymethyl-5-[hydroxymethyl-di)oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane.

The preferred compounds for use in surface-coating compositions are those in which the total number of oxymethylene (--CH₂ O--) units in one or more of the substituents on the oxazolidine ring is not greater than six. While compounds having more than six oxymethylene units in their ring substituents are very effective in controlling the growth of bacteria and fungi, they tend to be somewhat unstable in surface-coating compositions and to impart to them the odor of formaldehyde. Examples of the preferred bicyclic compounds include polyoxymethyleneoxazolidines in which

i. the substituent in the 5-position is --(CH₂ O(CH₂ O)₁₋₄ -CH₂ OH and the substituents in the 2- and 8-positions are hydrogen, alkyl, phenyl, or halophenyl;

ii. the substituent in the 5-position is --CH₂ OCH₂ OCH₂ OH, that in the 2-position is --(CH₂ O)₀₋₂ CH₂ OH, and that in the 8-position is hydrogen, alkyl, phenyl, or halophenyl; and

iii. the substituent in the 5-position is --CH₂ O(CH₂ O)₁₋₂ -CH₂ OH and the substituents in the 2- and 8-positions are --CH₂ OH.

The biocidal compounds of this invention may be prepared by any suitable and convenient procedure. For example, they may be prepared by the reaction of the appropriate oxazolidine with formaldehyde and/or paraformaldehyde. Alternatively, they may be prepared by the reaction of an aminoalcohol with formaldehyde and/or paraformaldehyde and optionally another aldehyde. These reactions are ordinarily carried out in aqueous solution at a temperature between about 20° and 100°C. When an aqueous formaldehyde solution is used, the reactions are preferably carried out at ambient temperature; when paraformaldehyde or a mixture of aqueous formaldehyde and paraformaldehyde is used, it is preferred that the reaction be carried out at a higher temperature.

Among the aminoalcohols that can be reacted with formaldehyde and, if desired, another aldehyde to form the novel polyoxymethyleneoxazolidines is tris(hydroxymethyl)aminomethane. The aminoalcohol is reacted with formaldehyde or a mixture of formaldehyde and a second aldehyde. The second aldehyde may be an aliphatic aldehyde, such as acetaldehyde, α-chloracetaldehyde, propionaldehyde, butyraldehyde, or 2-ethylbutyraldehyde; an aromatic aldehyde, such as benzaldehyde, p-chlorobenzaldehyde, or 2,4-dichlorobenzaldehyde; a dialdehyde, such as glyoxal, succinaldehyde, or glutaraldehyde; or a mixture of these aldehydes.

The reaction products may be recovered from the aqueous solutions in which they are formed and purified by known techniques. In most cases the products are mixtures comprising polyoxymethyleneoxazolidines having the structural formula set forth hereinbefore.

Particularly advantageous results have been obtained when the aqueous solutions of polyoxymethyleneoxazolidines resulting from the reactions previously described are used without separation or purification of the biocidal compound or additional treatment other than adjustment of the concentration of the biocidal component to the desired level to protect suface-coating compositions from attack by bacteria and fungi. In addition to costing less than the purified polyoxymethyleneoxazolidines and being easier to incorporate into aqueous surface-coating compositions, the aqueous solutions, which contain 20 percent to 80 percent and preferably 40 percent to 60 percent by weight of one or more of the aforementioned polyoxymethyleneoxazolidines, provide better biocidal activity for a given concentration of the polyoxymethyleneoxazolidine in the surface-coating composition. Unlike most other aqueous surface-coating compositions that contain a biocide, the surface-coating compositions to which the aqueous polyoxymethyleneoxazolidine solutions have been added tend to become lighter in color on aging.

The polyoxymethyleneoxazolidines of this invention can be used to impart bacterial and fungal resistance to a wide variety of surface-coating compositions including both water-based and organic solvent-based coating systems.

The polyoxymethyleneoxazolidines are preferably used as the biocide in aqueous surface-coating compositions that contain about 10 percent to 60 percent by weight of a water-insoluble, film-forming, resinous binder that is an oleoresinous binder, a synthetic linear addition polymer, or a mixture of these binders. The useful aqueous dispersions of synthetic linear addition polymers are ordinarily prepared by the emulsion polymerization of ethylenically-unsaturated monomers. Illustrative of these polymers are polyvinyl acetate; polyvinyl butyrate; polyvinyl chloride; copolymers of vinyl acetate with vinyl chloride or acrylonitrile; copolymers of vinyl chloride with vinylidene chloride; polyethylene; polyisobutylene; polystyrene; copolymers of styrene with maleic anhydride or butadiene; copolymers of acrylonitrile with butadiene; copolymers of methacrylic acid esters of alcohols having 1 to 8 carbon atoms with vinyl acetate, vinyl chloride, acrylonitrile, or styrene; copolymers of acrylic acid esters of alcohols having 1 to 8 carbon atoms with vinyl acetate, vinyl chloride, acrylonitrile, or styrene; and mixtures thereof. Suitable oleoresinous binders including drying oils, such as linseed oil, tung oil, soybean oil, dehydrated castor oil, safflower oil, or fish oil; bodied drying oils; blends of drying oils or bodied drying oils with a resin component such as limed rosin, an ester gum, or phenolic resin; oleoresinous varnishes formed by heating one of the aforementioned resins with one or more drying oils or bodied drying oils; alkyd resins, which are resinous products resulting from the reaction of a polyhydric alcohol, such as pentaerythritol or glycerol, with a dicarboxylic acid, such as phthalic anhydride, and fatty acids; and mixtures thereof.

The polyoxymethyleneoxazolidines can also be used as the biocide in organic solvent-based systems that contain an oleoresinous binder as hereinbefore defined.

The addition to surface-coating compositions of as little as 0.1 percent by weight of one or more of the biocidal compounds of this invention will bring about an appreciable improvement in the resistance of the composition to attack by fungi and bacteria. Three percent or more of the biocidal compounds can be used, but these larger amounts ordinarily do not provide further improvement in the properties of the surface-coating compositions and for this reason are not usually used. The amount of the biocidal compound that will provide optimum protection for a surface-coating composition depends upon such factors as the choice of the biocidal compound, the choice of resinous binder and other ingredients of the composition and the amount of each of these materials that is used, and the application for which the coating composition is intended. In most cases 1 percent to 2 percent of polyoxymethyleneoxazolidine, based on the weight of the composition, is used to protect surface-coating compositions from attack by fungi. From 0.1 percent to 0.5 percent of a polyoxymethyleneoxazolidine, based on the weight of the composition, is preferably incorporated into aqueous surface-coating compositions to protect them from attack by bacteria.

In addition to the resinous binder and the biocidal compound, the surface-coating compositions may contain various auxiliary materials, such as pigments, extenders, solvents, dyes, defoaming agents, driers, thickeners, emulsifiers, plasticizers, other biocides, and the like in the amounts ordinarily used for these purposes.

The biocidal compounds may be incorporated into the surface-coating compositions by any suitable procedure. As has been indicated hereinbefore, the best results are obtained when aqueous solutions of the polyoxymethyleneoxazolidines are added to aqueous surface-coating compositions. Alternatively, the biocidal compounds can be combined with the pigments and other components to form a pigment phase that is mixed with the resinous binder and water or organic solvent to form the surface-coating composition.

The invention is further illustrated by the following examples.

EXAMPLE 1

A mixture of 60.5 grams (0.5 mole) of tris(hydroxymethyl)aminomethane, 121.5 grams (1.5 moles) of 37% aqueous formaldehyde solution, and 31.6 grams (1.0 mole) of 95% paraformaldehyde was stirred and heated at its reflux temperature until a homogeneous solution was obtained. The solution was cooled and filtered. There was obtained 213 grams of a clear yellow solution that contained 43.1% of water and 56.9% of solids. The pH of an 0.1 M solution of the product was 6.6. The product was shown by NMR, IR, and GC analysis of its silyl ethers to be a mixture of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane, 5-hydroxymethoxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane, and 5-hydroxymethylpolyoxymethylene-1-aza-3,7-dioxabicyclo(3.3.0)octanes having the structural formula ##EQU3## wherein x represents numbers in the range of 1 to 3.

EXAMPLE 2

A mixture of 60.5 grams (0.5 mole) of tris(hydroxymethyl)aminomethane, 121.5 grams (1.5 moles) of 37% aqueous formaldehyde solution, and 47.3 grams (1.5 moles) of 95% paraformaldehyde was stirred and heated at its reflux temperature until a homogeneous solution was obtained. The solution was cooled and filtered. There was obtained 229.3 grams of a clear yellow solution that contained 40.1% of water and 59.9% of solids. The pH of an 0.1 M solution of the product was 6.6. The product was shown by NMR, IR, and GC analysis of its silyl ethers to be a mixture containing about 20% of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane, 37% of 5-hydroxymethoxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane, 14% of 5-[hydroxymethyl-di(oxymethylene)]-1-aza-3,7-dioxabicyclo-(3.3.0)octane, 21% of 5-[hydroxymethyl-tri(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane, and 8% of 5-[hydroxymethyl-tetra-(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane.

EXAMPLE 3

A mixture of 29.0 grams (0.2 mole) of 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane and 32.4 grams (0.4 mole) of 37% aqueous formaldehyde solution was stirred at ambient temperature until a homogeneous solution was obtained. The product was an aqueous solution that contained 26.1% of water 73.9% of 5-[hydroxymethyl-di(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)-octane. The pH of an 0.1 M solution of the product was 6.9.

EXAMPLE 4

A. A polyvinyl acetate latex paint was prepared by mixing together the following materials:

                          Parts by Weight                                          ______________________________________                                         Water                   481.5                                                  25% Aqueous solution of sodium salt of                                                                 24                                                     maleic anhydride/diisobutylene copolymer                                       Potassium pyrophosphate 3                                                      Long chain fatty acid alkanolamide                                                                     9                                                      Defoamer                6                                                      Ethylene glycol         75                                                     11/4 % Aqueous solution of hydroxy-                                                                    375                                                    ethylcellulose                                                                 Aqueous emulsion containing 55% of poly-                                                               1299                                                   vinyl acetate                                                                  Diethyl ether of diethylene glycol                                                                     30                                                     Titanium dioxide        690                                                    Talc                    345                                                    Calcium metasilicate    150                                                    ______________________________________                                    

This paint had the following properties as determined by standard paint testing procedures:

    Viscosity            65 K.U.                                                   Brookfield Viscosity 800 cps.                                                  (No. 4 spindle, 60 rpm)                                                        pH                   7.8                                                       Yellowness Index     3.0                                                  

Small amounts of the biocidal compounds of this invention or comparative biocides were added to portions of this paint.

B. An acrylic latex paint was prepared by mixing together the following materials:

                           Parts by Weight                                         ______________________________________                                         Water                    168                                                   Alkyl aryl ether surfactant                                                                             6                                                     25% Aqueous solution of sodium salt of                                                                  27                                                    maleic anhydride/diisobutylene copolymer                                       Defoamer                 12                                                    2% Aqueous solution of hydroxyethyl-                                                                    300                                                   cellulose                                                                      Ethylene glycol          60                                                    Titanium dioxide         750                                                   Mica (waterground)       90                                                    Calcium carbonate        375                                                   Ammonium hydroxide (28%) 6                                                     Aqueous dispersion containing 46% acrylic                                                               1642                                                  ester copolymer (66% ethyl acrylate,                                           32.5% methyl acrylate, and 1.5% acrylic acid)                                  ______________________________________                                    

This paint had the following properties:

    Viscosity             72 K.U.                                                  Brookfield Viscosity (No. 3                                                                          1250                                                     spindle, 60 rpm) (cps)                                                         Yellowness index      2.6                                                      pH                    9.2                                                 

Small amounts of the biocidal compounds of this invention or comparative biocides were added to portions of this paint.

C. An exterior house paint was prepared by mixing together the following materials:

                     Parts by Weight                                               ______________________________________                                         Basic lead carbonate                                                                              288                                                         Zinc oxide         232                                                         Titanium dioxide (rutile)                                                                         149                                                         Talc               260                                                         Linseed oil        242                                                         Bodied linseed oil 114                                                         Mineral spirits    114                                                         Antiskinning agent 2                                                           Manganese naphthenate (6%)                                                                        2.27                                                        Lead naphthenate (24%)                                                                            11.3                                                        ______________________________________                                    

Small amounts of the biocidal compounds of this invention or comparative biocides were added to portions of this paint.

D. The polyvinyl acetate latex paint, the acrylic latex paint, and the oil-based paint were evaluated by means of an agar diffusion assay. In this test, agar is inoculated with the test organism, the treated paint is placed in a well cut from the agar, and after incubation at 28°C. and 85-95% relative humidity, the activity of the biocide is measured by zones of inhibition. The biocidal compounds tested and the results obtained are given in the table that follows. In this table

    ZO        =     Zone of inhibited growth in mm.                                O         =     No zone of inhibition; no growth                               Tr        =     Trace zone of inhibited growth                                 --        =     Not tested                                                     Bacteria A                                                                               --    Mixed paint spoilage strains                                   B         --    Pseudomonas aeruginosa                                         C         --    Aerobacter aerogenes                                           Fungi D   --    Pullularia pullulans                                           E         --    Penicillium crustosum                                          F         --    Aspergillus niger                                         

                                      Table                                        __________________________________________________________________________     Activity of Polyoxymethyleneoxazolidines                                       as Biocides in Paints                                                                            Test                 Biocidal Activity                                         Level                                                                              Effect on Liquid Paint                                                                          Bacteria     Fungi                      Biocide      Paint                                                                               (%) pH Odor                                                                               Color                                                                              Viscosity                                                                             A   B   C   D   E   F                  __________________________________________________________________________     Product of Ex. 1                                                                            PVA  2   7.3                                                                               None                                                                               None                                                                               None  ZO-20                                                                              ZO-10                                                                              ZO-14                                                                              ZO-20                                                                              ZO-9                                                                               ZO-2                                  1   7.4                                                                               "   "   "     ZO-17                                                                              ZO-8                                                                               ZO-10                                                                              ZO-10                                                                              ZO-8                                                                               ZO-1                                  0.5 7.4                                                                               "   "   "     ZO-15                                                                              ZO-5                                                                               ZO-8                                                                               ZO-5                                                                               ZO-5                                                                               0                                     0.1 7.4                                                                               "   "   "     ZO-7                                                                               ZO-3                                                                               ZO-1                                                                               0   0   0                                Acrylic                                                                             2   7.7                                                                               "   "   Gelled                                                                               ZO-24                                                                              ZO-9                                                                               ZO-10                                                                              ZO-19                                                                              ZO-7                                                                               ZO-1                                  1   7.9                                                                               "   "   None  ZO-11                                                                              ZO-2                                                                               ZO-4                                                                               ZO-3                                                                               ZO-4                                                                               Tr                                    0.5 8.5                                                                               "   "   "     ZO-5                                                                               Tr  ZO-1                                                                               0   0   0                                     0.1 9.1                                                                               "   "   "     0   0   0   0   0   0                                Oil  2   -- "   "   "     --  --  --  ZO-4                                                                               ZO-3                                                                               ZO-2                Product of Ex. 2                                                                            PVA  2   7.3                                                                               None                                                                               None                                                                               None  ZO-22                                                                              ZO-14                                                                              ZO-14                                                                              ZO-30                                                                              ZO-11                                                                              ZO-3                                  1   7.4                                                                               "   "   "     ZO-18                                                                              ZO-8                                                                               ZO-14                                                                              ZO-10                                                                              ZO-8                                                                               ZO-2                                  0.5 7.4                                                                               "   "   "     ZO-15                                                                              ZO-7                                                                               ZO-11                                                                              ZO-5                                                                               ZO-5                                                                               Tr                                    0.1 7.4                                                                               "   "   "     ZO-7                                                                               ZO-4                                                                               ZO-5                                                                               Tr  ZO-1                                                                               0                                Acrylic                                                                             2   7.6                                                                               "   "   "     ZO-20                                                                              ZO-9                                                                               ZO-13                                                                              ZO-21                                                                              ZO-9                                                                               ZO-3                                  1   7.8                                                                               "   "   "     ZO-12                                                                              ZO-4                                                                               ZO-7                                                                               ZO-5                                                                               ZO-4                                                                               Tr                                    0.5 8.4                                                                               "   "   "     ZO-7                                                                               ZO-2                                                                               ZO-1                                                                               Tr  0   0                                     0.1 9.1                                                                               "   "   "     Tr  0   0   0   0   0                                Oil  2   -- "   "   "     --  --  --  ZO-7                                                                               ZO-5                                                                               ZO-3                Product of Ex. 3                                                                            PVA  2   6.8                                                                               None                                                                               None                                                                               Gelled                                                                               ZO-15                                                                              ZO-8                                                                               ZO-10                                                                              ZO-20                                                                              ZO-8                                                                               ZO-1                                  1   7.2                                                                               "   "   None  ZO-15                                                                              ZO-9                                                                               ZO-9                                                                               ZO-14                                                                              ZO-5                                                                               Tr                                    0.5 7.3                                                                               "   "   "     ZO-13                                                                              ZO-7                                                                               ZO-8                                                                               ZO-8                                                                               ZO-2                                                                               Tr                                    0.1 7.5                                                                               "   "   "     ZO-6                                                                               ZO-2                                                                               Tr  0   0   0                                Acrylic                                                                             2   7.3                                                                               "   "   "     ZO-14                                                                              ZO-7                                                                               ZO-9                                                                               ZO-15                                                                              ZO-8                                                                               ZO-2                                  1   7.5                                                                               "   "   "     ZO-11                                                                              ZO-5                                                                               ZO-8                                                                               ZO-8                                                                               ZO-3                                                                               0                                     0.5 8.1                                                                               "   "   "     ZO-5                                                                               ZO-1                                                                               ZO-3                                                                               0   0   0                                     0.1 8.6                                                                               "   "   "     Tr  0   0   0   0   0                                Oil  2   -- "   "   "     --  --  --  ZO-7                                                                               ZO-7                                                                               ZO-1                Comparative Examples                                                           5-Hydroxymethyl-1-aza-                                                                      PVA  2   7.5                                                                               None                                                                               None                                                                               None  ZO-3                                                                               ZO-4                                                                               ZO-1                                                                               ZO-4                                                                               ZO-2                                                                               0                   3,7-dioxabicyclo                                                                            Acrylic                                                                             2   8.4                                                                               "   "   "     ZO-11                                                                              ZO-3                                                                               ZO-4                                                                               ZO-6                                                                               0   0                   (3.3.0)octane (51.2%                                                                        Oil  2   -- "   "   "     --  --  --  0   Tr  0                   aqueous solution)                                                              S-13 (Dow    PVA  2   7.5                                                                               None                                                                               None                                                                               None  ZO-13                                                                              0   0   ZO-14                                                                              ZO-19                                                                              ZO-12               Chemical Co.)                                                                               Acrylic                                                                             2   9.1                                                                               "   "   "     ZO-13                                                                              0   0   ZO-20                                                                              ZO-11                                                                              ZO-5                             Oil  2   -- "   "   "     --  --  --  ZO-20                                                                              ZO-10                                                                              ZO-6                Bis(phenylmercuric)-                                                                        PVA  2   7.0                                                                               None                                                                               None                                                                               None  ZO-19                                                                              ZO-11                                                                              ZO-9                                                                               ZO-13                                                                              ZO-10                                                                              ZO-15               dodecenyl succinate                                                                         Acrylic                                                                             2   9.0                                                                               "   "   "     ZO-17                                                                              ZO-13                                                                              ZO-8                                                                               ZO-10                                                                              ZO-3                                                                               ZO-10               (Super Ad-it)                                                                               Oil  2   -- "   "   "     --  --  --  ZO-17                                                                              ZO-6                                                                               ZO-14               (Tenneco Chemicals,                                                            Inc.)                                                                          NOne         PVA  --  7.5                                                                               None                                                                               None                                                                               None  0   0   0   0   0   0                                Acrylic                                                                             --  9.3                                                                               "   "   "     0   0   0   0   0   0                                Oil  --  -- "   "   "     --  --  --  0   0   0                   __________________________________________________________________________

The superiority as biocides for surface-coating compositions of the polyoxymethyleneoxazolidines of this invention over a closely-related substituted oxazolidine is apparent from a comparison of the biocidal data for the products of Examples 1-3 with those for 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane. The products of Examples 1 and 2, which are mixtures of substituted oxazolidines that contain the comparator 5-hydroxymethyl-1-aza-3,7-dioxabicyclo(3.3.0)octane as well as the 5-hydroxymethylpolyoxymethylene-1-aza-3,7-dioxabicyclo(3.3.0)octanes of this invention, were substantially more effective against bacteria and fungi than the comparator. Similarly, it is shown in the table that the product of Example 3 is more active at the 0.5% level in the PVA paint and at the 1% level in the acrylic paint than the comparator at the 2% level.

Each of the other bicyclic polyoxymethyleneoxazolidines disclosed herein can be used in a similar way to protect surface-coating compositions from attack by bacteria and fungi. 

What is claimed is:
 1. A bicyclic polyoxymethyleneoxazolidine having the structural formula ##EQU4## wherein n represents a number in the range of 1 to
 4. 2. A polyoxymethyleneoxazolidine as defined in claim 1 that is 5-[hydroxymethyl-di(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane.
 3. A polyoxymethyleneoxazolidine as defined in claim 1 that is 5-[hydroxymethyl-tri(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane.
 4. A polyoxymethyleneoxazolidine as defined in claim 1 that is 5-[hydroxymethyl-tetra(oxymethylene)]-1-aza-3,7-dioxabicyclo(3.3.0)octane. 